Volume kinetics of intravenous crystalloid and colloid solutions in healthy, isoflurane-anesthetized rabbits.

HES provides greater fluid potency and longer intravascular persistence than LRS in anesthetized rabbits.

This prospective, randomized crossover study investigated the volume kinetics of two commonly used intravenous fluids—lactated Ringer's solution (LRS), a crystalloid, and 6% tetrastarch 130/0.4 (HES), a colloid—in 10 healthy, isoflurane-anesthetized rabbits. Each animal received 25 mL/kg of LRS and 6.25 mL/kg of HES infused over 20 minutes, with a minimum 14-day washout period between treatments. Serial hemoglobin, RBC count, and hematocrit measurements were used as surrogate markers for plasma dilution and served as inputs for microconstant volume kinetic modeling. Both fluids produced comparable peak plasma dilution, validating the conventional 4:1 potency ratio of crystalloids to colloids. LRS demonstrated rapid distribution and elimination, with half-lives of approximately 4.6 and 57.8 minutes, respectively. In contrast, HES exhibited markedly prolonged distribution and elimination half-lives of approximately 53.5 and 231.0 minutes, reflecting its greater intravascular persistence. The pharmacokinetic profiles observed in rabbits were consistent with data reported in other mammalian species, supporting the translational relevance of this model. The study confirms that volume kinetic analysis is a feasible and informative tool for characterizing fluid behavior in anesthetized rabbits. Limitations include the absence of urine volume measurements, which would refine elimination estimates. These findings have practical implications for fluid therapy planning in rabbit anesthesia, particularly in optimizing fluid selection and dosing strategies during surgical and critical care settings.

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